Not applicable.
The present invention generally relates to composite structures, and more particularly, to a venting system for venting and/or filtering airflow entering/exiting at least a portion of a composite structure.
Composite materials (such as those utilized in aircrafts, spacecrafts, watercrafts, and the like) are generally made up of a pair of outer face sheets and an inner core area. The outer face sheets can be made from a variety of materials such as, but not limited to, metals, carbon fiber reinforced plastic, and glass fiber reinforced plastic. In addition, these outer face sheets may be single layer or multi-layered structures. The cores of these composite materials are generally designed to be lightweight, yet provide structural integrity to the composite material. Due to the inherent structural characteristics of these core areas, air is inevitably trapped within them between the face sheets during fabrication of these composite materials and/or during a subsequent apparatus construction process (e.g., integrating the composite material into an aircraft, spacecraft, or watercraft).
Air trapped within the core areas of these composite materials tends to be problematic (amongst other instances) when utilizing these composite materials as components of an aircraft and/or spacecraft. More specifically, the pressure differential of the air trapped between the face sheets of the composite material and the air outside the composite tends to increase with elevation. This phenomenon, also referred to as xe2x80x9cascent induced pressure decayxe2x80x9d, increases the risk of face sheet delamination due to pressure induced bond line failures. In other words, since air pressure inside the composite material may be greater than the air pressure outside the composite material (generally a function of distance from the Earth""s surface), the outer face sheet may be pushed away from the core of the composite material by air pressure buildup, potentially resulting in damage to the composite material (and hence the aircraft/spacecraft).
Some attempts at addressing the problems associated with pressure differences between the core areas of composite materials and the external environment (e.g., the atmosphere) have included installing one or more vents on the interior face sheet of the composite material that faces the inner cavity of the fuselage or payload compartment of the aircraft/spacecraft. These xe2x80x9cinteriorxe2x80x9d vents potentially pose serious risks to sensitive payloads due to the presence of contaminants and debris (which are generally byproducts of the trimming and/or drilling steps of the composite material fabrication process) within the core area of the composite material. Other attempts have included the use of vents that are made from stainless steel screens reinforced by aluminum frames. These reinforced stainless steel and aluminum vents are generally affixed to vent holes in composite structures. However, these vents tend to be very expensive, difficult to integrate/install, and are generally uniquely designed for one particular application.
The present invention is generally directed to a system for venting composite materials. More specifically, the present invention is generally directed to a low cost venting system that is easily integrated directly onto/into face sheets of a wide variety of composite structures. Any appropriate type/configuration of composite structure may benefit from utilizing the venting system of the present invention. One particularly desirable application of the venting system is in the outer shell of a launch vehicle, an aircraft, a spacecraft, a rocket, or any other aerodynamic body that flies or otherwise travels through gaseous medium.
A first aspect of the invention relates to a venting assembly including a venting system and a composite structure (e.g., the composite material or an aircraft or spacecraft). Herein, reference to a xe2x80x9ccomposite structurexe2x80x9d or xe2x80x9ccomposite materialxe2x80x9d generally refers to a structure/material having at least first and second face sheets and a core disposed between the first and second face sheets. These face sheets may each include one or more layers of material (i.e., may be composite structures themselves). The venting system of the first aspect generally includes a mounting assembly and a non-metallic venting medium. The mounting assembly generally enables the venting system to be interconnected with the composite structure at a first location and at least generally fluidly interconnected with a first air hole extending from an outermost extent of the composite structure at least within the core of the composite structure. In other words, the venting system may be associated with one of the face sheets in such a manner that the first air hole is at least substantially, and more preferably entirely, covered by the venting system. Alternatively, the venting system may be attached to an apparatus that is attached to the composite structure in such a manner that the first air hole is at least substantially covered by the apparatus, and that an apparatus hole in the apparatus fluidly interconnects the air hole of the composite structure with the venting system of the first aspect.
The venting medium of the first aspect of the present invention is generally capable of one or both filtering and controlling airflow at least between the core of the composite structure and an exterior environment (e.g., the atmosphere). The venting medium generally includes a perimeter region and an airflow region disposed inwardly of the perimeter region, and is designed in such a manner that the airflow region of the venting medium is generally free from direct contact with any other portion of the venting system. In other words, the airflow region of the venting medium generally does not touch the mounting assembly or any other component of the venting system.
Various refinements exist of the features noted in relation to the subject first aspect of the present invention as well. Further features may also be incorporated in the subject first aspect of the present invention as well. These refinements and additional features may exist individually or in any combination. The airflow region in one embodiment of the venting medium may include a surface area of at least about 45 mm2. This surface area of the airflow region is generally defined by a major surface of the airflow region (i.e., a surface that is generally parallel to a lateral extent of the composite material) minus the cross-sectional areas (taken at the major surface) of corresponding airflow passages disposed therethrough. Some embodiment of the first aspect may include the venting medium having a filter mesh size ranging from about 3 microns up to about 5 microns; however, filter mesh sizes outside this range may be appropriate. The individual airflow passages of the airflow region in the case of the first aspect (and optionally, the perimeter region) of the venting medium may have cross-sectional areas ranging in size from about 7 microns2 up to about 20 microns2. In other words, in the case of the airflow passages being substantially circular, the cross-sectional diameter of the airflow passages may range from about 3 microns up to about 5 microns. In the case of the airflow passages exhibiting a polygonal, elliptical, or irregular (multi-angled and/or multi-radial) configuration, at least one cross-sectional length extending between two different points along the configuration may fall within the previously stated range of 3 microns up to about 5 microns. In some embodiments of this first aspect, it may be appropriate to utilize a venting medium having airflow passages outside the above-disclosed range.
The venting medium of one embodiment of this first aspect may generally exhibit an outgassing characteristic quantified by a maximum Total Mass Loss (TML) of no more than about 1%. In other words, an amount of material, which makes up venting medium, that may be lost when exposed to an outer space environment may be no more than about 1%. In another embodiment, the venting medium of this first aspect may generally exhibit an outgassing characteristic quantified by Collected Volatile Condensable Material (CVCM) of no more than about 0.1%. In other words, an amount of material, which makes up the venting medium, that may be lost when the venting medium is exposed to a vacuum environment may be no more than about 0.1%. In any event, these outgassing characteristics generally comply with ASTM (American Society for Testing and Materials) E595 standards.
In one embodiment of the first aspect, the venting medium may be made up of a fluorocarbon polymer or copolymer. In another embodiment, the venting medium may be made up of a fluoroethylene polymer or copolymer. In yet another embodiment, the venting medium may be made of polytetrafluoroethylene, tetrafluoroethylene-hexa-fluoro-propylene copolymer, and combinations thereof The venting medium may exhibit one or more physical properties/characteristics, such as a warp tensile strength of at least about 200 lbs./in., a fill tensile strength of at least about 175 lbs./in., or both. Herein, xe2x80x9cwarp tensile strengthxe2x80x9d generally refers to the amount of force per unit length the primary threads/fibers of the venting medium can withstand without significant damage. Similarly, xe2x80x9cfill tensile strengthxe2x80x9d generally refers to the amount of force per unit length the secondary threads/fibers (i.e., those fibers/threads that are oriented generally transversely to the primary threads/fibers) of the venting medium can withstand without significant damage (e.g., breaking). One embodiment of the venting medium may have a thickness ranging from about 5 mils up to about 10 mils. Another embodiment of the venting medium may have a thickness of about 1.5 mils plus a thickness of a fabric to which it is attached/bonded. However, one or more embodiments of the first aspect may have a thickness outside the above-disclosed thickness ranges, as an appropriate thickness of the venting medium may be dependent upon a variety of factors including, but not limited to, the tensile strength and/or the modulus of elasticity of the material utilized to make up the venting medium, the surface area of the airflow region of the venting medium, and the density of the airflow apertures associated with the venting medium. In one embodiment, the venting medium may be sufficient in strength to withstand a pressure of up to about 30 pounds per square inch. In another embodiment, the venting medium may be sufficient in strength (i.e., have one or both a sufficient warp tensile strength and a sufficient fill tensile strength) to withstand a pressure of at least 14.5 pounds per square inch. The mounting assembly in the case of the first aspect of the present invention may have a variety of appropriate configurations, but is preferably cylindrical in shape. In one embodiment, the mounting assembly may have male threads at least on an outer surface thereof for engaging female threads associated with the first face sheet or an apparatus attached thereto. In other words, the mounting assembly may be screwed into an affixed engagement with the first face sheet of the composite structure. Besides the use of threadings, the mounting assembly may be attached to the composite structure utilizing any appropriate manner of attachment such as, but not limited to, welds, adhesives, screws, pins, bolts, and combinations thereof. In one embodiment, the venting medium may be attached to this mounting assembly only at the perimeter region of the venting medium. In other words, the mounting assembly may avoid direct contact with the airflow region of the venting medium. Stated another way, the interface between the venting medium and the mounting assembly may be limited to a perimeter region of the venting medium.
In one embodiment of the first aspect, a retention assembly may be utilized for fastening the venting medium to the mounting assembly. This retention assembly may have a first inner diameter and the mounting assembly may have a second inner diameter. The first inner diameter of the retention assembly may be substantially equal to the second inner diameter of the mounting assembly. An outermost extent of the airflow region of the venting medium may be substantially aligned with at least one of a first inner extent of the retention assembly and a second inner extent of the mounting assembly. Take for example the case where the mounting assembly is a cylinder having a first annular opening extending therethrough, and the retention assembly is a cylinder having a second annular opening extending therethrough. An outermost extent of the airflow region of the venting medium may be substantially aligned with the circumference(s) of one or both the first and second annular openings. The venting medium may be attached to the retention assembly only at the perimeter region of the venting medium. In other words, the retention assembly may avoid direct contact with the airflow region of the venting medium. The perimeter region of the venting medium may be positioned between (i.e., xe2x80x9csandwichedxe2x80x9d by) the mounting assembly and the retention assembly. Adhesive may be disposed between the mounting assembly and the perimeter region of the venting medium to adhere the mounting assembly to the perimeter region of the venting medium. Similarly, adhesive may be applied between the retention assembly and the perimeter region of the venting medium to adhere the retention assembly to the perimeter region of the venting medium. Appropriate adhesives for adhering the venting medium to one or both the retention and mounting assemblies may include, but are not limited to, epoxy, acrylic, urethane, and hot melt adhesives.
One or both the mounting assembly and the retention assembly of the first aspect may be made up of metal such as, but not limited to, stainless steel, titanium, aluminum, and alloys and combinations thereof. By contrast, in another embodiment one or both the mounting assembly and the retention assembly of the first aspect may be made up of an appropriate thermoplastic or thermosetting plastic. A xe2x80x9cthermoplasticxe2x80x9d, as used herein, may generally refer to a polymer, and in some variations a high polymer (i.e., an organic macromolecule composed of a large number of monomers and generally having a molecular weight of at least about 5000), that softens when exposed to heat and returns to its original condition when cooled. Examples of thermoplastics may include, but are not limited to, polyvinyl chloride, nylons, fluorocarbons, linear polyethylene, polyurethane prepolymer, polystyrene, polypropylene, and cellulosic and acrylic resins. A xe2x80x9cthermosetting plasticxe2x80x9d, as used herein, generally refers to a polymer, and in some variations a high polymer, that solidifies or sets irreversibly when heated usually via a cross-linking reaction of the molecular constituents induced by heat or radiation. In cases where a thermosetting plastic is used, it may be necessary to add xe2x80x9ccuring agentsxe2x80x9d such as organic peroxides or sulfur (e.g., in the case of a rubber based thermosetting plastic). For example, linear polyethylene may be cross-linked to a thermosetting material either by radiation or by chemical reaction. Phenolics, alkyds, amino resins, polyesters, epoxides, and silicon are usually considered to be thermosetting, but the term may also apply to materials where additive-induced cross-linking is possible (e.g., natural rubber). Those features discussed herein in relation to one or more of the other aspects of the present invention may be incorporated into this or any other aspect of the present invention as well, and in the manner noted herein.
A second aspect of the invention relates to a venting assembly having a venting system interfacing with a composite material (that may or may not be associated with an aircraft or spacecraft). The venting system of this second aspect substantially provides a controlled fluid interconnection between the interior of the core and the atmosphere. In other words, in this second aspect, for airflow to pass between the exterior environment and the core of the composite material, the airflow must pass through the venting system. The venting system of this second aspect generally includes a mounting assembly for mounting the venting system with respect to an air hole of the composite material. In other words, the venting system may be mounted directly to a face sheet or may be attached to another structure that is attached to the composite material. In any event, the airflow that passes through the first air hole and between the core of the composite material and the exterior enviromnent generally must pass through the venting medium of the venting system of the second aspect. Generally this venting medium of the second aspect is made up of a fluorocarbon polymer or copolymer and optionally, those materials that do not materially affect the physical and/or chemical characteristics/properties of the fluorocarbon polymer/copolymer.
Various refinements exist of the features noted in relation to the subject second aspect of the present invention as well. Further features may also be incorporated in the subject second aspect of the present invention. These refinements and additional features may exist individually or in any combination. In one embodiment, the venting medium may be made up of a fluoroethylene polymer or copolymer. For example, the venting medium may be made up of polytetrafluoroethylene, tetrafluoroethylene-hexa-fluoro-propylene copolymer, and/or combinations thereof.
One embodiment of the venting medium of this second aspect may have airflow passages extending entirely therethrough. Stated another way, airflow passing between the exterior environment and the core of the composite material of one variation of the second aspect generally must pass through these airflow passages. One embodiment of the venting medium of the second aspect may have a thickness ranging from about 5 mils up to about 10 mils. Another embodiment of the venting medium of the second aspect may have a thickness of about 1.5 mils plus a thickness of a fabric to which it is attached/bonded. The venting medium of the second aspect may (at least in one embodiment) be sufficient in strength (i.e., warp and/or fill tensile strength) to withstand a pressure of up to about 30 pounds per square inch. In another embodiment, the venting medium of the second aspect may be sufficient in strength to withstand a pressure of at least 14.5 pounds per square inch.
The venting medium, in the case of this second aspect may include a perimeter region and an airflow region disposed inwardly of the perimeter region. In one embodiment, the airflow region of the venting medium is free from direct contact with any other portion of the venting system. The venting medium may be attached to the mounting assembly of the second aspect only at the perimeter region of the venting medium. Various features discussed herein in relation to one or more of the aspects of the present invention may be incorporated into any of the other aspects of the present invention as well, and in the manner noted herein.